It has heretofore been known to produce polyesters and copolymers having high slip, this property being defined as the lack of affinity between two polyester surfaces when in contact with each other.
Two approaches have been used to produce polyesters having high slip. One is to incorporate into the polymer various non-homogeneous substances having low coefficients of friction, such as clays, silicon dioxide, etc. Another is to incorporate into the molecular chain a substance which imparts the non-slip characteristic to the polyester. This latter approach is the subject of U.S. Pat. No. 4,348,510, granted Sept. 7, 1982. In this application, the use of various polysiloxanes is disclosed.
The use of clays and other non-homogeneous substances have been found wanting in that they affect clarity of the polyester, have poor dispersion characteristics, and that they would show up on X-ray film.
Similarly, the use of various polysiloxanes to achieve high slip, while allowing high clarity and being incorporated into the polyester, has heretofore required a conditioning step to produce the desired effect. This involved the procedure outlined in ASTM test method D-1894 calling for the polyester film to be maintained in an inert atmosphere at 75.degree. F. and 55 percent relative humidity for at least 40 hours. Without this conditioning step, the silicone modified polyester would not possess high slip properties. On a large production basis, this process would become highly undesirable as it would entail great expenditure in large amounts of treating equipment.
U.S. Pat. No. 4,310,600 to Cross discloses the use of a silicon coating on a biaxially oriented polyester film. There is no teaching or suggestion in this patent or in the prior art of a process for producing immediate high slip polyester film.